1850 Bişgin: Journal of AOAC International Vol. 101, No. 6, 2018
Food Composition and Additives
Simultaneous Preconcentration and Determination of Brilliant Blue and Sunset Yellow in Foodstuffs by Solid-Phase Extraction Combined UV-Vis Spectrophotometry Abdullah Taner Bişgin
Niğde Ömer Halisdemir University, Ulukışla Vocational School, 51900 Niğde, Turkey
Background: Brilliant Blue and Sunset Yellow, two highly water-soluble synthetic food dyes, are the most popular food dyes used and consumed. Although they are not highly toxic, some health problems can be observed when excessive amounts of food products containing these dyes are consumed. Objectives: The aim of the study was to develop a simultaneous UV-Vis combined solidphase extraction method, based on the adsorption onto Amberlite XAD-8 resin, for determination of Brilliant Blue and Sunset Yellow dyes. Methods: Sample solution was poured into the reservoir of the column and permitted to gravitationally pass through the column at 2 mL/min flow rate. Adsorbed dyes were eluted to 5 mL of final volume with 1 mol/L HNO3 in ethanol solution by applying a 2 mL/min flow rate. Dye concentrations of the solution were determined at 483 and 630 nm for Sunset Yellow and Brilliant Blue, respectively. Results: The detection limits of the method for Brilliant Blue and Sunset Yellow were determined as 0.13 and 0.66 ng/mL, respectively. Preconcentration factor was 80. Brilliant Blue contents of real food samples were found to be between 11 and 240 μg/g. Sunset Yellow concentrations of foodstuffs were determined to be between 19 and 331 μg/g. Conclusions: Economical, effective, and simple simultaneous determination of Brilliant Blue and Sunset Yellow was achieved by using a solid-phase extraction combined UV-Vis spectrometry method. Highlights: The method is applicable and suitable for routine analysis in quality control laboratories without the need for expert personnel and high operational costs because the instrumentation is simple and inexpensive.
F
ood dyes have been widely used in the textile, soap and detergent, automobile, cosmetic, pharmaceutical, and food industries for coloring products and giving them an attractive appearance (1). Brilliant Blue (BB; E133) and Sunset Yellow (SY; E110) are highly water-soluble synthetic food dyes
used to color bakery goods, beverages, candies, jellies, sausage, and numerous other foods, as well as cosmetics and drugs (2). These are the most popular, widely used, and consumed food dyes (3). The World Health Organization has defined daily intake values of 6 mg/kg for BB and 4 mg/kg for SY on the basis of human body weight (4, 5). They can cause hyper sensitivity (allergy-like) reactions in some consumers and might trigger hyperactivity in children when they are consumed in excessive amounts in food (6). Therefore, it is very important to detect and determine BB and SY contents of foodstuffs with acceptable sensitivity and accuracy. Various scientific instruments including UV-Vis spectrophotometer (7), HPLC column (8), electrochemical analyzer (9), mass spectrometer (10), and fluorescence spectrometer (11) have been used for detection and determination of the dyes. However, some problems, such as the interference effect of the matrix and very low dye concentration of samples, could arise in the determination process without pretreatment of the samples (12). Therefore, analytical chemists have made great efforts to develop more sensitive separation, purification, extraction, and preconcentration methods, such as cloud point extraction (CPE; 13), solid-phase extraction (SPE; 14–17), dispersive liquid-liquid microextraction (DLLME), liquidliquid microextraction (18), and membrane filtration (19). SPE combined UV-Vis spectrophotometry is very simple and practical among these instrument techniques and methods. The use of a UV-Vis spectrophotometer does not require a highly experienced and skilled analyst. UV-Vis spectrophotometric analysis offers simplicity and lower operational cost than other instruments. On the other hand, the SPE method offers high extraction performance, low detection limit, and high preconcentration factor. Moreover, solid phase has high adsorption capacity and can be used many times by regeneration with appropriate solvent. These features make the method more attractive and preferable compared with other methods and techniques (20–24). The aim of the study was to develop a simultaneous UV-Vis combined SPE method, based on the adsorption onto Amberlite XAD-8 resin, for determination of BB and SY, the most widely used and consumed food dyes. The method was successfully applied to foodstuffs to determine their BB and SY contents. Materials and Methods
Received March 14, 2018. Accepted by SG April 4, 2018. Corresponding author’s e-mail:
[email protected] Color images are available online at http://aoac.publisher. ingentaconnect.com/content/aoac/jaoac DOI: https://doi.org/10.5740/jaoacint.18-0089
Chemicals Amberlite XAD-8, an aliphatic macroreticular cross-linked commercial resin, has 310 m2/g surface area and 0.78 mL/g porosity and was purchased from Sigma-Aldrich. SY, BB, and
Bişgin: Journal of AOAC International Vol. 101, No. 6, 2018 1851 other chemicals used were purchased from Merck and SigmaAldrich. Distilled water was used in all aqua dilutions. All solutions used in the experiments were stored in a refrigerator at 4°C. Phosphate buffers (H3PO4–NaH2PO4) for pH = 2–3, acetate buffers (HAc–NaAc) for pH = 4–5, and phosphate buffers (NaH2PO4–Na2HPO4) for pH = 6–8 were used. Instruments Shimadzu Model UV-160A double-beam UV-Vis spectrophotometer was used for measurements of absorbance and absorption spectra (Shimadzu Corporation, Kyoto, Japan). pH of the buffer and sample solutions was measured and controlled with Hanna Model HI-2211 digital pH meter (Hanna Instruments, Woonsocket, RI). Surface micrographs of the resins were taken by using Olympus Model SZ61 stereomicroscope (Olympus Corporation, Tokyo, Japan) combined with Nikon D90 camera (Nikon Corporation, Tokyo, Japan). Column SPE Procedure A mini chromatographic glass column with 500 mL of reservoir and Teflon stopcock was used in the separation process. The column was 1 cm in diameter and 10 cm in height. A 500 mg amount of Amberlite XAD-8 resin was slurred with water and poured into the column. The loaded column was washed sequentially with ethanol, water, methanol, water, 1 M HNO3 in methanol, and water to remove inorganic and organic impurities. The loaded column bed height was approximately 1 cm. Amounts of 4 μg BB and 10 μg SY were added to 25 mL of sample solution, which was buffered to pH 4. The colored sample solution was poured into the reservoir of the column and permitted to gravitationally pass through the column at 2 mL/min flow rate. Adsorbed dyes on the resin were gravitationally eluted to 5 mL of final volume with 1 mol/L HNO3 in ethanol solution by applying a 2 mL/min flow rate. Dye concentrations of the solution were determined at 483 nm and 630 nm for SY and BB, respectively. Pretreatment of Food Samples Adequate amounts of energy drink, candy, jelly, drink powder, syrup, marshmallow, and peppermint samples were dissolved in water. A warming process in ultrasonic water bath was used for complete dissolution of candy, marshmallow, jelly, peppermint, and drink powder samples. Blue band filter paper was used for the filtration process. Filtrates were diluted to an appropriate sample volume. The pH levels of the aqueous samples were adjusted to pH 4 by the addition of acetate buffer solution. Energy drink and syrup samples were directly applied to the method after pH adjustments and necessary dilutions.
equilibrium between dye and resin was reached, the suspension was centrifuged. Final concentrations of solutions were determined with the spectrometer at 483 nm and 630 nm for SY and BB, respectively. Results and Discussion Optimum parameters of the method for simultaneous extraction and determination of BB and SY dyes were investigated. UV-Vis spectra of the dyes are shown in Figure 1 with their molecular structures. Influence of pH on the Simultaneous Extraction One of the important factors in the SPE studies for dye is pH of the sample solution. pH of aqueous media provides optimum conditions for quantitative retention of dye molecules on the resin by protonation or deprotonation of both resin and dye. The pH effect was examined in the range of pH 2–8. Results are shown in Figure 2a with SDs. Quantitative extractions for both dyes were obtained between pH 3 and 5. A pH of 4 was chosen as the optimum and working pH. Influence of Sample Flow Rates on the Extraction Retention of dye on the resin is important for quantitative extraction. Quantitative adsorption of dye depends on the sample flow rate. Therefore, the sample flow rate for both dyes was investigated between 1 and 10 mL/min. Results are shown in Figure 2c with SDs. Quantitative extractions of both dyes were obtained up to 3 mL/min flow rate. Thus, the sample flow rate was optimized as 2 mL/min. Influence of Eluent Flow Rates on the Extraction Complete desorption of dye molecules from resin is important for quantitative extraction and depends on the flow rate of eluent solution. To obtain quantitative desorption and find the optimum flow rate, eluent solution was passed through the column at eluent flow rates of between 1 and 10 mL/min. Results are shown in Figure 2d with SDs. Quantitative extraction values were obtained for both food dyes between 1 and 3 mL/min. The optimum eluent flow rate was chosen as 2 mL/min, and this optimum parameter was applied in all subsequent experiments.
Adsorption Experiments Batch adsorption experiments were performed separately for each dye to determine adsorption mechanisms and behavior of the method. Adsorption experiments were conducted in a 25 mL beaker at room temperature by using pH 4 buffer solution and contacting 50 mg of Amberlite XAD-8 resin. After adsorption
Figure 1. UV-Vis spectra of 2.00 μg/mL of SY, 0.75 μg/mL of BB, and a mixture of 4.00 μg/mL of SY and 1.50 μg/mL of BB.
1852 Bişgin: Journal of AOAC International Vol. 101, No. 6, 2018 a)
b)
c)
d)
Figure 2. (a) Effect of pH (n = 3), (b) sample volume (n = 3), (c) sample flow rate (n = 3), and (d) eluent flow rate (n = 3).
Effect of Eluent Type on the Simultaneous Extraction
Effect of Sample Volume Sample volume is the most effective parameter to obtain low detection limits and high preconcentration factors. Sample volume was investigated in a range from 25 to 600 mL. Results are shown in Figure 2b with SDs. Recovery results were quantitative for both dyes up to 400 mL of sample volume. Quantitative extractions for both dyes were not observed at higher than 400 mL. According to the highest sample volume that could be obtained as the quantitative and final volume, the preconcentration factor was obtained as 80 for both dyes.
Polarities of eluent solutions are an important factor because adsorbed dye molecules on the resin must be eluted completely from the resin to attain quantitative extraction values. Therefore, mixtures of organic solvents and various acids were used. Results are comparatively given in Figure 3 with a bar graph. Quantitative extraction was achieved in the presence of 0.5 M HNO3 in methanol and ethanol, and 0.5 M and 1.0 M HCl in methanol. In view of low toxicity, economic considerations, and availability of the chemicals, 0.5 M HNO3 in ethanol was chosen as the optimum eluent solution.
Figure 3. Effect of different eluents on the simultaneous extraction (n = 3).
Bişgin: Journal of AOAC International Vol. 101, No. 6, 2018 1853 determination of SY and BB can be performed using the proposed method.
Effect of Matrix Components In this part of the study, effects of potential interfering organic and inorganic components were investigated. Results are shown in Table 1 with SDs and tolerable concentrations. Interfering species at the concentrations given in Table 1 did not positively or negatively affect the simultaneous determination of SY and BB. These results show that simultaneous, reliable Table 1. Matrix effect of the interfering components (n = 3) Concn, mg/L Ion/dye
Rec., %a
Added as
SY
BB
SY
BB
3-
Na3PO4
1000
1000
99 ± 2
96 ± 2
SO4
2-
Na2SO4
100
100
97 ± 4
99 ± 2
-
NaCl
1000
1000
98 ± 3
98 ± 4
NO3
NaNO3
1000
1000
98 ± 2
97 ± 2
Na
+
NaNO3
1000
1000
97 ± 3
96 ± 4
Co
2+
Co(NO3)2.6H2O
100
100
99 ± 3
98 ± 3
Cu
2+
Cu(NO3)2.5H2O
100
100
96 ± 1
96 ± 2
Al(NO3)3.9H2O
50
50
96 ± 2
98 ± 6
KNO3
1000
1000
98 ± 2
97 ± 2
Cd(NO3)2.6H2O
100
100
98 ± 3
100 ± 4
PO4 Cl
-
Al K
3+
+
Cd
2+
3+
Cr(NO3)3.3H2O
25
25
98 ± 4
99 ± 2
2+
Ni(NO3)2.6H2O
100
100
100 ± 3
99 ± 2
2+
Pb(NO3)2
100
100
95 ± 1
96 ± 3
2+
Mg(NO3)2.6H2O
1000
1000
94 ± 4
95 ± 1
2+
CaCl2
1000
1000
97 ± 3
99 ± 2
2+
Mn(NO3)2.4H2O
100
100
99 ± 3
97 ± 2
Basic yellow
—
0.4
0.4
100 ± 2
101 ± 3
Tartrazine
—
0.5
0.5
102 ± 3
99 ± 3
Quinoline yellow
—
0.3
0.3
101 ± 3
100 ± 2
Cr Ni
Pb
Mg Ca
Mn
a
Mean ± SD.
b
— = No data.
b
Effect of Resin Amount on the Extraction To obtain simultaneous quantitative extraction of the dyes, the column was loaded with various amounts of resin in the range of 100–600 mg. Results are shown comparatively in Figure 4a with SDs. Recovery values of the dyes increased with increasing resin amounts up to 500 mg and then reached maximum and constant levels. Quantitative extractions of the dyes were obtained using a minimum of 500 mg of resin. Therefore, the column was loaded with 500 mg of Amberlite XAD-8 resin, and this resin amount was used in subsequent experiments. Surface Micrographs of the Resin To demonstrate the single and simultaneous adsorption of dyes onto Amberlite XAD-8 resin, both pure and colored resin micrographs were taken. Micrographs are shown in Figure 4b. White granules are pure resin. Orange and blue granules are SY and BB adsorbed statuses of the resin. Turquoise blue granules are a mixture of SY and BB adsorbed status of the resin. All colored granules show that BB, SY, and a mixture of them were well adsorbed onto the Amberlite XAD-8 resin. Adsorption Isotherm and Mechanism for Simultaneous Extraction Adsorption isotherm was plotted separately for each of the dyes. Experimental results were obtained and calculations were performed to fit Langmuir and Freundlich adsorption isotherm models. Perfect compatibilities were observed with the Freundlich model. Adsorption isotherms related to adsorption of SY and BB are shown in Figure 4c and 4d, respectively. According to the isotherm results, retention of the both dyes onto resin is by physical and multilayer adsorption. The relationship between dye molecules and resin can be explained by weak electrostatic forces and hydrophobic interactions. In the Freundlich model, the high correlation coefficients obtained
Figure 4. (a) Effect of resin amount (n = 3), (b) surface micrographs, (c) adsorption isotherm for SY, and (d) adsorption isotherm for BB.
1854 Bişgin: Journal of AOAC International Vol. 101, No. 6, 2018 for both dyes and dark colored resin samples suggested that adsorption takes place on a heterogeneous surface through a multilayer adsorption mechanism (20). Applications of Real Samples To observe applicability of the method in different matrixes, the method was applied to different natural drinking water samples. Analyte addition-recovery tests for BB and SY dyes were also performed by adding 1.00–2.00 and 2.00–4.00 μg for BB and SY, respectively. Results are shown in Table 2 with SDs. Quantitative and satisfactory recovery results were obtained between 99 and 101%. Different solid and liquid foodstuff samples containing BB food dye were analyzed and their BB contents were determined. Results are shown in Table 3 with SDs. Analyte addition-recovery tests were also performed. Amounts of
1.00 μg and 2.00 μg BB dye were added to real samples. Relative recovery values were obtained between 96 and 101%. Addition-recovery tests results are shown in Table 4 with SDs. SY contents of various liquid and solid food samples were determined. SY concentrations of food samples are shown in Table 3 with SDs. Amounts of 2.00–4.00 μg of SY dye were added to real food samples to perform analyte addition-recovery tests. Quantitative relative recovery values were in the range between 96 and 103%. Results are shown in Table 5 with SDs. Determined BB and SY concentrations are shown in Table 3 with SDs. Results are shown as μg/g and μg/mL for solid and liquid samples, respectively. BB contents of foodstuffs were determined between 11 and 240 μg/g and between 5 and 142 μg/mL for solid and liquid samples, respectively. SY concentrations of food samples were determined between 19 and 331 μg/g for solid samples. Liquid syrup sample SY content was determined as 24.27 μg/mL.
Table 2. Analyte addition/recovery tests on the simultaneous extraction of BB and SY (n = 3) Found, μga
Add, μg Sample
BB
Natural spring water from Koyunlu Natural spring water from Hançerli Tap water from Niğde
Analytical Characteristics and Performance of the Method Rec., %a
SY
BB
SY
BB
SY
—
—
BDLc
BDL
—
—
1.00
2.00
1.01 ± 0.02
2.00 ± 0.02
101 ± 2 100 ± 2
2.00
4.00
2.03 ± 0.04
4.01 ± 0.03
101 ± 4 100 ± 3
b
—
—
BDL
BDL
—
—
1.00
2.00
0.99 ± 0.02
1.98 ± 0.04
99 ± 2
99 ± 2
2.00
4.00
2.01 ± 0.04
3.96 ± 0.05
100 ± 4 99 ± 3
—
—
BDL
BDL
1.00
2.00
1.00 ± 0.02
1.98 ± 0.02
100 ± 2 99 ± 2
2.00
4.00
1.99 ± 0.03
3.98 ± 0.04
99 ± 3
a
Mean ± SD.
b
— = No data.
—
— 99 ± 3
Added, μg
BDL = Below detection limit.
Table 3. BB and SY contents of foodstuffs (n = 3) Concn, μg/mLa
Syrup
BB
SY b
BDL
24.27 ± 0.29
Energy drink
5.76 ± 0.12
BDL
Citrus syrup
142.49 ± 5.72 Concn, μg/g
Bear jelly
Table 4. Analyte addition/recovery tests for determination of BB in foodstuffs (n = 3) Sample
c
Sample
The detection limits of the method for BB and SY were determined as 0.13 and 0.66 ng/mL, respectively. LOQ values were determined as 0.38 and 1.94 ng/mL for BB and SY, respectively. Preconcentration factors of the method for the both dyes were equal and 80. Relative standard deviations (RSDs) for BB and SY were 3.5 and 4.5, respectively. Linear dynamic ranges of the method were determined as 0–4.5 with an equation of y = 0.1364 x + 0.0024 (R2 = 0.9995) and 0–10.0 with an equation of y = 0.0388 x + 0.0037 (R2 = 0.9994) for BB and SY, respectively.
BDL a
Found, μg
Relative rec.
Found, μg
Relative rec.
—b
1.90 ± 0.08
—
1.7 3 ± 0.04
—
2.52 ± 0.07
—
1.00
2.90 ± 0.04 100 ± 5 2.73 ± 0.02 100 ± 4 3.54 ± 0.04 101 ± 6
2.00
3.84 ± 0.06 97 ± 2
a
Mean ± SD.
b
— = No data.
3.69 ± 0.02
98 ± 1 4.46 ± 0.08 96 ± 7
Table 5. Analyte addition/recovery tests for determination of SY in foodstuffs (n = 3)
35.01 ± 0.63 BDL
Marshmallow
120.92 ± 0.70
BDL
Tight sugar
240.71 ± 4.36
BDL
Orange juice powder
BDL
331.90 ± 8.69
—b
Sesame sugar
BDL
21.67 ± 1.01
2.00
Worm jelly
BDL
19.49 ± 1.08
4.00
b
Pepperminta
Relative rec.
BDL
a
Energy drinka
Found, μg
11.38 ± 0.33
Peppermint
Citrus syrupa
Sample Added, μg
Bear jellya Found, μg
Orange juice a powder
Syrupa
Relative rec.
Found, μg
3.17 ± 0.06
—
4.85 ± 0.06
5.15 ± 0.06
99 ± 1
6.83 ± 0.06
99 ± 1 6.20 ± 0.06 100 ± 5
7.30 ± 0.10 103 ± 2 8.85 ± 0.06
99 ± 2 8.06 ± 0.06 96 ± 4
Mean ± SD.
a
Mean ± SD.
BDL = Below detection limit.
b
— = No data.
Relative rec.
Found, μg
Relative rec.
—
4.19 ± 0.11
—
Bişgin: Journal of AOAC International Vol. 101, No. 6, 2018 1855 Table 6. Comparison of the developed method with reported methods on extraction and determination of BB and SY Sample treatment c
SPE
CPE
Extractive agent
Food dye
Detection system
Matrix
LOD, μg/L
LDR, μg/mL
PFb
RSD, %
Ref.
β-Cyclodextrin polymer
BB
UV-Vis
Drinks, gum, juice powder
16.0
0.05–12.0
5
3.4
(25)
TX-100
BB
UV-Vis
Beverages, drinks, custard
3.00
0.02–1.30
—e
4.6
(26)
[C10MIM][BF4]
BB
UV-Vis
Candy, drinks, jelly, ice cream
0.34
0.00–0.15
38
0.8
(27)
Monolithic column with CN phase
BB
HPLC
Beer samples
20.0
0.50–200
—
1.1
(28)
d
DLLME
f
SPE
a
CPE
Triton X-100
BB
UV-Vis
Jelly, candy
16.0
0.05–3.50
10
3.3
(29)
CPE
Triton X-100
SY
UV-Vis
Soft drink, sweet, gelatin
5.00
0.02–0.45
33
1.5
(30)
SPE
Amberlite XAD-1180 and XAD-16
SY
UV-Vis
Syrup, fruit juice powder
2.00
0.20–20.0
60
7.0
(31)
CPE
Triton X-100
SY
UV-Vis
Jelly, pastel, candy, smarties
9.00
0.02–4.00
10
3.5
(32)
SPE
Polyacrylamide composite
SY
UV-Vis
Fruit juice, beverage, cocktail
37.0
0.00–0.25
17
3.9
(33)
CPE
Triton X-100, Triton X-114, Brij 56
SY
UV-Vis
Beverages
10.4
20.0–120
2
3.0
(34)
SPE
Amberlite XAD-8
BB
UV-Vis
Energy drink, marshmallow, candy, jelly, syrup, fruit juice
0.13
0.00–4.50
80
3.5
Present study
SPE
Amberlite XAD-8
SY
UV-Vis
Energy drink, marshmallow, candy, jelly, syrup, fruit juice
0.66
0.00–10.0
80
4.5
Present study
a
LDR = Linear dynamic range.
b
PF = Preconcentration factor.
c
SPE = Solid-phase extraction.
d
CPE = Cloud point extraction.
e
— = Not available.
f
DLLME = Dispersive liquid-liquid microextraction.
Comparison study with other methods is shown in Table 6. When the proposed method was compared with previously reported methods, the achieved preconcentration factor of 80 was higher than others. Detection limits for both dyes were lower than in other reported studies. RSDs of BB and SY were at levels comparable with other methods. To evaluate performance, precision, and accuracy of the method, different amounts and mixtures of BB and SY were analyzed in real samples. Interday and intraday precision were determined from the analysis of three replicates. Results are shown in Table 7. Conclusions In this study, economical, effective, and simple simultaneous determination of BB and SY was achieved by using an SPE combined UV-Vis spectrometry method. The developed method represents the wide linear ranges, low detection limits, and high preconcentration factors for both food dyes. Amberlite XAD-8 resin allows for simultaneous extraction of dyes from complex matrixes. The proposed method presented effective separation of anions and cations with high selectivity ratios. The only disadvantage of the method is that the procedure has not permitted effective separation of another dye. The experimental results and data demonstrate that simultaneous, reliable determination of SY and BB in food
Table 7. Interday and intraday precision results for determination of BB and SY (n = 3) Added, μg
Found
BB
SY
1.00
Relative rec.
RSD, %
BB
SY
BB
SY
—
BB
SY
—
0.96
—
96.05
—
2.41
—
2.00
—
1.95
—
97.53
—
3.28
1.00
2.00
0.97
1.99
97.08
99.51
2.13
2.45
98.32
—
2.21
—
Interday a
Intraday 1.00
—
0.98
—
—
2.00
—
1.97
—
98.44
—
1.00
2.00
0.99
1.98
99.07
98.78
2.28
a
3.65 3.79
— = No data.
samples can be performed using the proposed method. In this work, a simple simultaneous SPE method that works gravitationally, without using any advanced equipment or pressure system, was developed. The method is applicable and suitable for routine analysis in quality control laboratories; it does not require expert personnel or result in high operational costs because instrumentation is simple and inexpensive. Furthermore, this study will be at the forefront for determination of food dye applications in the near future.
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